Surely that isn’t right. My little 12x10 foot greenhouse uses 5kwh on a cold night to stay above freezing using a little 800 watt space heater that cycles off and on.
Edit: nope I checked and that is a correct number.
Wow, I really thought desalination would be something like factor 10 more energy expensive.
Regarding your greenhouse: Does it sit flat on the earth? I'm thinking about lowering the greenhouse at my parents house somewhat into the earth, I think 2 feet would already help with keeping it warmer...
No it just sits on the ground. I went down a whole rabbit hole recently about how to keep a greenhouse warm in winter. Being below ground would probably help somewhat.
I did the math and used a kill a watt to monitor the usage and just doing a little space heater hooked to an Inkbird temperature controller was plenty economical for me. I have cheap electricity where I live though. About 30 cents a night when it is freezing outside. So absolutely worst case scenario would be $9 a month which I can handle for how much joy it gives me to be able to grow plants in the winter.
Look at energy requirements of desal vs. fresh water pollution proliferation.
10-14 kwh required to desal 1000 gallons of water.
50% of world's food supply is powered by proliferation of phosphorus and nitrogen rich fertilizer and their corresponding runoff.